Multigun cathode-ray tube



Sept. 21, 1954 .1. c. FRANCKEN MULTIGUN CATHODE-RAY TUBE Filed Nov. 13,1952 T r I c IL A N Z w Y a a 000 DOGOOOO Patented Sept. 21, 1954MULTIGUN CATHODE-RAY TUBE Jan Carel Francken, Einclhoven, Netherlands,assignor to Hartford National Bank and Trust Company, Hartford, Conn, astrustee Application November 13, 1952, Serial No. 320,271

Claims priority, application Netherlands November 28, 1951 3 Claims.

This invention relates to cathode-ray tubes,

more particularly, to multi-gun cathode-ray tubes for color televisionreception or for the simultaneous recording of two or more values.

One form of color television system commonly employed utilizes threedistinct electron guns located in the neck of a cathode-ray tube. Thetelevision signal for exciting such a tube is generally broken down intoseparate channels for the red, green and blue components "of the colorimage, each of the colors energizing one of the electron guns. In orderfor the color image to accurately correspond to the transmittedimage,the picture on the fluorescent screen at one end of the cathode-ray tubeis built up by a composite of these three primary color pictures. Thesesystems usually also employ an apertured grid located in front of theluminescent screen in a position to intercept the electron beams inorder to direct the beams at particular areas or points of theluminescent screen, the electron beam of each of the electron guns beingrequired to pass through a. single aperture of the grid or strike atabout the same point on the luminescent screen. That is to say, not onlymust the beam axes intersect at a single aperture or at the luminescentscreen, but also each of the beams must be focussed at that aperture orat the screen.

The main object of the invention is to provide a simple apparatus,externally mounted on a multi-gun cathode-ray tube, for directing and/orfoscussing the individual beams of the guns so that they impinge upon aluminescent screen at about the same point without requiring great carein the manufacturing or positioning of the guns themselves.

According to the invention, a cathode-ray tube comprising a luminescentscreen supported at one end thereof and including a neck portion locatedat the opposite end is provided with a plurality of distinct electronguns. Each of the electron guns is housed ina separate cylindrical tube,the tubes being arranged substantially parallel to one another and beingconnected to the neck portion of the tube. Focussing and directioning ofthe beams of the electron guns is effected by providing a magneticdevice constituted by a pair of plane, substantially parallel plates ofmagnetic material having apertures therein for mounting said device onthe cylindrical tubes housing the electron guns. Hollow slideablepole-members are provided in each of the apertures of one of the platesand surrounding the cylindrical tubes of the electron guns forindividual focussing of the guns. A single, common,

electrical winding positioned between the plates energizes the magneticdevice.

The arrangement according to the invention has the advantage that thespace occupied thereby is materially smaller than that occupied by thepreviously-known arrangements. Moreover, accurate focussing anddirectioning of the beams is obtained in a very simple manner therebyeliminating the need for careful manufacturing and positioning of theguns.

The invention will now be described with reference to the accompanyingdrawing in which:

Fig. 1 shows a cathode-ray tube according to the invention forreproducing color television images;

Fig. 2 is a longitudinal section of a magnetic system of poles accordingto the invention for simultaneous production of the focussing fields ina multi-gun tube;

Fig. 3 is a cross-sectional view of the device shown in Fig. 2 in aplane at right angles to Fig. 2.

The cathode-ray tube shown in Fig. 1 comprises a wall I enclosing aluminescent screen 2 covered with a mosaic of superficial elementsconsisting of fluorescent materials of the kinds which becomeluminescent in the desired colors upon being excited by electrons. Agrid 3 comprising a large number of small apertures is provided in thevicinity of the screen 2.

Three substantially parallel electron guns each producing a directedelectron beam, are provided in the neck of the tube for scanning thescreen 2. The beams produced by the guns are directed to a common pointon an aperture in the grid 3 and in the case of parallel arrangement ofthe electron guns, the required convergence of the beams may be producedby the use of a focussing coil 4.

Each of the tubes 5, 6, and 1 contains an electrode gun, only that intube 5 being shown diagrammatically, comprising a cathode 8, a controlelectrode 9 and an anode Ill. A set of deflection coils l I forhorizontal deflection of the beam and a set of deflection coils [2 forvertical deflection thereof are provided on the tube.

In the construction of the collecting or luminescent screen 2 and thegrid 3, use, alternatively, may be made of a grid constituted byparallel wires, the different luminescent substances being provided onthe screen in lines having a width corresponding to the spacing betweenthe grid wires. The electron guns may be arranged in a straight lineside by side at right angles to the direction of the grid wires.However, in the embodiment shown in Fig. 1, the guns are arranged in theform of a triangle.

The beams from the three guns are focussed by the magnetic device shownin detail in Figs. 2 and 3 comprising a system of pairs of magneticpoles which are energized by a common electrical winding I3 when thelatter is traversed by electric current. In the particular embodimentshown in Figs. 2 and 3, two circular parallel plates l4 and I5 areconnected together by an annular upright edge I6 provided along theirouter circumferences. Both the plates I4, 15 and the upright edge l6 areconstituted by magnetic material. A single energizing winding I3 isarranged between the plates [4, l5 near their outer edges. Each platel4, l5 contains three apertures I1 and I8, respectively, by means ofwhich the device may be slipped over the tubes 5, 6, '1 comprising theelectron guns. Three hollow, adjustable pole members l9. eachconstituted by magnetic material, are in threaded engagement,respectively, with each of the apertures in the plate l5. These polemembers [9, each of which surround an electron gun, may be screwed inand out of the plate [5 to a greater or smaller extent so that thedistance between the pole member l9 and the plate [4 varies and, hence,the strength of the magnetic field therebetween for focussing eachindividual beam.

The energizing of the coil winding I3 will. pro- 3 duce magnetic fieldsbetween each pole member [9 and the plate M, the strength and focussingaction of these fields being dependent upon the position of the polemembers I9 which are individually adjustable for each electron gun.Consequently, with the above-described arrangement, the focal point anddirection of the electron beams produced by each of the electron gunsare individually adjustable by a magnetic device energized by a singlewinding with great accuracy.

While I have thus described my invention with specific examples andembodiments thereof, other modifications will be readily apparent tothose skilled in the art without departing from the spirit and the scopeof the invention as defined in the appended claims.

What I claim is:

1. A multi-gun cathode-ray tube for producing a plurality of directedelectron beams which impinge at about the same point on a collectingscreen, comprising an envelope supporting the collecting screen at oneend thereof and including a cylindrical neck portion located at theopposite end, a plurality of electron guns, a plurality of distinctcylindrical tubes each housing one of said guns, said cylindrical tubesbeing substantially parallel to one another and being connected to saidneck portion of said cathode-ray tube, and a magnetic device fordirecting said beams, said magnetic device comprising a plurality ofpairs of magnetic poles each in proximity of one of said guns, and asingle coil winding surrounding all of said pairs of poles forenergization thereof.

2. A multi-gun cathode-ray tube as claimed in claim 1 in which saidmagnetic device comprises a pair of plane parallel magnetic plates forforming said pairs of magnetic poles and having apertures therein forengagement with said cylindrical tubes, said winding being positionedbetween said plates, and a magnetic member uniting said plates alongtheir outer edges and enclosing said winding.

3. A multi-gun cathode-ray tube as claimed in claim 2 in which aplurality of adjustable sleeves of magnetic material are provided eachof which is in engagement with one of said apertures in one of saidplates and surrounds one of said guns for individually focussing eachgun.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 2,165,028 Blumlein July 4, 1939 2,170,944 Glass Aug. 29, 19392,407,667 Kircher Sept. 17, 1946 2,631,259 Nicoll Mar. 10, 1953

